For a liquid crystal display device used in mobile phone and personal digital assistant (PDA), a reduction in thickness is demanded. In addition, there is also a strong demand for making the screen larger while keeping the overall size smaller, namely, making it in the so-called narrow frame form. The small liquid crystal display device uses a light emitting diode (LED) as a light source of a backlight. However, the method of arranging the LED, the method of supplying electric current to the LED, and the use efficiency of the light from the LED are problems when trying to reduce the thickness and overall size of the liquid crystal display device.
In the configuration disclosed in JP-A No. 128820/2007, an LED is provided on a side surface of a light guide panel. A reflective sheet is provided on the back side of the light guide panel. The thickness of a portion of the reflective sheet is reduced, in which an LED flexible wiring sheet is provided to supply power to the LED.
In the configuration disclosed in JP-A No. 344851/2003, an LED is mounted on a main flexible wiring substrate attached to a liquid display panel. The main flexible wiring substrate is folded toward the back side so that the LED is provided on a side surface of the light guide panel. In JP-A No. 344851/2003, at this time, a light shielding pattern is formed in a portion of the back side of the main flexible wiring substrate to prevent the light of the LED from leaking to the outside through the main flexible wiring substrate.
In the method described above, the LED mounted on the main flexible wiring substrate is placed on a side surface of the light guide panel by folding the main flexible wiring substrate toward the back side of the light guide panel. However, this method has a problem in that it is difficult to obtain sufficient accuracy of the LED arrangement. In order to solve this problem, the following method has been proposed. There are separately formed two substrates, one is a main flexible wiring substrate attached to a liquid crystal display panel, and the other is an LED flexible wiring substrate for supplying power to the LED. Then, the main flexible wiring substrate and the LED flexible wiring substrate are attached to each other. This method can facilitate the LED to be placed at appropriate place in the light guide panel, without being constrained by the position of the main flexible wiring substrate.
In this case, the LED flexible wiring substrate is fixed to a portion of the light guide panel. The main flexible wiring substrate is fixed to a mold on which the liquid crystal display panel is mounted. Because the setting of the LED flexible wiring substrate and the main flexible wiring substrate at appropriate locations is prioritized, interference may occur between the electronic component mounted on the main flexible wiring substrate, and the LED mounted on the LED flexible wiring substrate.
The electronic component, solder around the connection, wiring, and the like, are formed to be exposed in the main flexible wiring substrate. Also the LED, solder around the connection, and the like, are formed to be exposed in the FED flexible wiring substrate. The main flexible wiring substrate and the LED flexible wiring substrate are arranged to overlap each other, and are finally attached to each other. In such a configuration, there may be a risk of short circuit between the electronic component, the solder around the connection, the wiring, and the like, in the main flexible wiring substrate, and the LED and the solder around the connection in the LED flexible wiring substrate.
This risk has been reduced by forming a partition wall between the portion of the electronic component mounted on the main flexible wiring substrate, and the portion of the LED, in order to prevent the electronic component from coming into contact with the LED, or with the solder around the connection and the like.
However, in this configuration, it is necessary to form the partition wall within the mold, thereby increasing the overall size of the mold. As a result, the overall size of the liquid crystal display device is increased. In addition, the space on both sides of the partition wall should be large enough to prevent the destruction of the LED or the electronic component due to the contact between the partition wall and the LED or the electronic component. This space requirement has caused a further increase in the overall size of the mold or in the overall size of the liquid crystal display device.